1. Field of the Invention
The present invention relates to a section mill for wells, and more particularly, to a section mill that permits a user to extend the cutting performance of the apparatus without retrieving it from the well.
2. Description of the Related Art
In the operation of oil wells, it is common during the maintenance stage to abandon the deepest portion of the casing (when it is in poor conditions) and open a casing window to install a new casing portion, typically, at an angle with respect to the previous casing, to reach oil deposits through a new path. Section mills are utilized to mill portions of a casing to accomplish this. In doing so, the casing needs to be cut from inside the casing and, subsequently, longitudinally reduced. The blades wear off and the conventional mills need to be retrieved to replace the blades and reinsert the mill.
Many designs for section mills have been designed in the past. The present invention includes a second set of blades that is deployed after the first set has been consumed milling the casing portion being replaced. This obviates the time consuming task of taking out the section mill assembly to change the used up set of blades and replace it with a new one.
Applicant believes that the closest reference corresponds to U.S. Pat. No. 5,074,355 issued to Lennon on Dec. 24, 1991 for a section mill with multiple cutting blades. Lennon's patented section mill for cutting through well casing includes multiple sets of cutting blades which are selectively engaged to continue cutting operations as blades dull. The cutting blade sets are selectively indexable such that as a first set dulls or fails a succeeding set can be utilized following retraction of the first set. The section mill also includes a central mandrel having offset cammed surfaces, which engage the cutting blades and cause them to expand outwardly. The mandrel is axially displaceable by a piston affected by hydraulic pressure. As the mandrel is axially displaced the indexed cutting blades are expanded by the cammed surface. Indexing is accomplished by a cam drum, which allows the mandrel to be rotated relative to the cutting blades in order to align the next cammed surfaces with their respective cutting blades.
However, it differs from the present invention because a mandrel for indexing the blades is not required. In the present invention the second set of blades is automatically deployed once the cut section of the casing is reached. Subsequently, the second (or other blades) will not be used until the first blade is completely worn off. This simpler approach eliminates several critical elements required in Lennon's section mill.
Other patents describing the closest subject matter provide for a number of more or less complicated features that fail to solve the problem in an efficient and economical way. None of these patents suggest the novel features of the present invention.